Backups & restore points · Versions and restoring
What do the file counts and sizes on each backup version mean?
Short answer: Each version lists its date and time, how many files it covers, how many were new, and how much data it added out of the total protected — showing how little each version costs.
Each version in Versions… shows when it was made, then a short summary: how many files it covers, how many were new in that version, and how much data it added compared with the total size of what it protects, written as the added amount "of" the total.
The "added" amount is the useful one for space: it shows how little each new version really costs, because unchanged files aren't stored again.